1. Field of Invention
This invention relates to a process for making quinacridones which are important commercial lightfast pigments and are extensively used in automotive finishes, textile printing and in architectural paints.
2. Description of the Prior Art
A commercially important process for making quinacridones involves the acid catalyzed ring closure of 2,5-diarylaminoterephthalic acids in polyphosphoric acid which is usually a preferred solvent for effecting the ring closure since it functions as both solvent and acid catalyst and is exemplified in U.S. Pat. No. 3,342,823 (Dien), U.S. Pat. No. 3,257,405 (Gerson et al.), U.S. Pat. No. 3,265,699 (Jaffe), and U.S. Pat. No. 3,940,349 (North). However, other solvents such as nitrobenzene can be used with an acid catalyst as disclosed in U.S. Pat. No. 3,020,279 (Woodlock), and still another process known in the prior art is exemplified in British patent Specification No. 978,091 (Sandoz) in which quinacridones are prepared by ring closing a 2,5-diarylaminoterephthalic acid in an organic solvent such as ethylene glycol with the aid of an acid catalyst. However, these prior art methods suffer from the disadvantage of using large quantities of expensive solvents which are difficult and/or hazardous to recover and which tend to create pollution problems.
It is an object of this invention to provide a simple and economical process for making quinacridone and its derivatives using a limited quantity of ethylene glycol solvent in the presence of an easily recoverable organic liquid.
It is also an object of this invention to make unsubstituted gamma quinacridone by a simple and economical process.
A still further object is to prepare solid solutions of quinacridone mixtures by a simple and economical process.
Other objects and advantages of the present invention will appear from the following embodiments and descriptions.